The test head of an electronic device test apparatus for testing semiconductor integrated circuit devices and other devices under test (DUT) contains pin electronic cards to which large numbers of various test-use devices which form high frequency circuits or power circuits for test use are mounted.
Among such test-use devices, there are ones which become high in temperature due to self generated heat. Therefore, the art of supplying a coolant to a water jacket which is attached to the pin electronics cards so as to cool the test-use devices has been known since the past (for example, see PLT 1).